Download playlist items in reverse order

Download playlist items in reverse order

Series of videos are typically uploaded to YouTube playlists in
chronological order.  By default, these videos are downloaded
latest-to-earliest; this is great for seeing the latest videos in a
series, but prevents streaming video in the order that the videos were
produced.  Add an option to download videos in reverse order,
earliest-to-latest.

Conflicts:
	youtube_dl/YoutubeDL.py
	youtube_dl/__init__.py